82 COMPARATIVE ANATOMY. 



XII. 



ANIMAL ELECTRICITY AND PHOSPHORESCENCE, 



ANIMAL ELECTRICITY. 



THE following are electrical animals : 



Fishes. Torpedo oculata; Raia batis; Raia clavata; Gym- 

 notus electricus; Malapterurus electricus; Tetraodon electricus; 

 Trichiurus electricus. 



Articulates. Scolopendra electrica. 



Torpedo oculata. The disk is somewhat broader than long, abruptly 

 rounded in front ; the tail is as long as the disk. The distance from the 

 beginning of the ventral fin to its free end is, as a rule, considerably smaller 

 than the distance from that to the end of the ventral fin. In the young 

 individual the border of the spiracle is surrounded with five to nine teeth; 

 these are lost in the more aged. The dorsal fins have rounded angles, and 

 convex or straight posterior borders. The caudal fin is either longer than 

 high or the length and height are equal. 



The coloration is subject to variation. The prevailing tint of the dorsal 

 region may be reddish brown with bluish spots around the eyes, varying in 

 number between seven and one. If a few of these alone be present they 

 are situated in the median line of back. Or the spots may be of a white 

 color, scattered over the region of back. These have a palish border, with 

 an intense central spot of a copper color. Or the points surrounding the 

 spiracles may be absent, and in place of the bluish spots a uniform brown 

 color be prevalent, with a few whitish spots scattered over the surface. 



Measurements. From the tip of nose to mouth, 1" 1"'; from the mouth 

 to anus, 5" 9'"; from anus to end of caudal fin, 5" 6'"; length of disk, 6" 

 3'"; breadth of disk, 7". Habitat. The Mediterranean Sea and Atlantic 

 Ocean. (Muller and Henle.) 



Anatomy of Electrical Organs. The electrical organs occupy a large 

 part of the broad expansions of the body, which in the other allied fishes 

 are formed only by the lateral fins. They form two separate masses, one on 

 either side of the head and gills. Each is an irregular ellipsoid, convex on 

 either side, its long diameter not quite parallel to the axis of the body, and 

 extending outward to the cartilaginous margins of the great fins, and poste- 

 riorly to the cartilage which separates the thoracic from the abdominal cavity. 

 Their form and the honeycomb embossments of their surfaces can be distin- 

 guished through the skin both of the dorsal and ventral aspects. The com- 

 mon integuments being removed, two strong fascial coverings are discovered 



